The southern region of São Paulo state, with an area of 500.000 hectares, and comprising the municipalities of Itapetininga, Itararé, Itaberá, Itapeva and São Miguel Arcanjo, is of low fertility but has aroused the interest of farmers because of the excellent topography and the proper climate for the cultivation of wheat (Triticum aestivum, L.) and soybeans (Glycine max (L) Merril). In order to study the reaction of the soybean to the application of chemical fertilizers containing nitrogen, phosphorus, potassium, calcium, sulphur and minor elements, an experiment was made in Engenheiro Bacelar distrit, municipality of Itapeva, on red soil ("terra-roxa") mixed with Glacial clay. The experiment wos designed to permit the study of the residual effects of the fertilizers too. The results obtained in this experiment indicated a strong favorable response to phosphorus and calcium and a limited reaction to potassium. They also showed a negative response to nitrogen ond o non-significant effect from use of sulphur and minor elements. A theoretical study was made concerning the economics of fertilizing with phosphorus, being verified that under the conditions of the present experiment the application of ordinary superphosphate directly to soybean brought returns. The considerable residual effect observed in the second year of the experiment indicated that this profit can be sufficient to increase the yield of subsequent plantings. On the other hand, the residual effect demonstrated in this experiment supports the view that the application of mineral fertilizers, especially of phosphorus, should be made to the annual crops that precede the soybean in a rotation program.